When adjusting a pulley make sure you have the proper amount of shims installed in the complete assembly. We recommend using at least 10 shims. It?s a good idea to start with too many shims so when the two halves are tightened together the belt is loose. To tighten the belt- remove shim washers from between the pulley halves one at a time re tightening the pulley halves each time to check tension. Proper tension should be about a half inch of deflection. Warning: if you tighten the pulley halves against the belt and not the shims you will break the inside half of the pulley . Store the leftover shim washers between the pulley outer half and the hat-shaped special washer.